Numerous linearization circuits exist for reduction of intermodulation (IM) signal distortion for power amplifiers (PAs) using real-time analog feedback. However, moderate and large bandwidth systems suffer from instability problems due to incidental circuit delays when present analog feedback systems are used to lower IM signal distortion.
While digital predistortion systems for power amplifiers avoid the instability problems of the analog feedback systems, digital systems typically require the use of look-up tables, where the look-up tables consist of an inverse mapping of the power amplifier non-linearity. The inverse mapping is applied to a linear input signal and results in a linearized power amplifier output. The look-up table is regularly updated to adapt to changing characteristics of the power amplifier, typically utilizing digital signal processing. An iterative error minimization algorithm seeking to minimize the difference between a reference and the power amplifier output is generally used for the digital signal processing. However, use of such an algorithm often results in convergence problems for an arbitrary power amplifier.
Thus, an alternative system and method are needed for acquiring gain coefficients for providing a predistorted drive signal for a nonlinear transmission path.